The invention relates to the field of basins dug out in the ground. More precisely, the invention relates to a safety anti-reversing device for a bottom of a basin in a ground that is able to be the seat of hydrostatic pressures liable to exert a thrust on this bottom. Being able to prevent a leakage flow in a first direction, from the basin to the ground, and to enable a filling flow in a second direction contrary to the first direction, the type of safety anti-reversing device in question comprises:                a body comprising communicating openings for passage of the filling flow, and        a flexible membrane supported by the body and deformable, due to the thrust force of a hydrostatic pressure in the ground, from a closed configuration in which this flexible membrane closes said openings in tight manner so as to prevent leakage flow, to a pass-through configuration in which the filling flow is enabled passing through the body via the communicating openings.        